Manuka honey, the New Zealand product long touted for wound care, may also hold potential against bacteria that cause respiratory infections, including strains resistant to common antibiotics, and its antibacterial effects arise from the combined action of methylglyoxal (MGO) and additional components within the honey matrix, according to new research led by Aston University.
Allcott et al. show that increasing UMF grade of Manuka honey is associated with stronger antibacterial activity and that this activity cannot be explained by sugar content or methylglyoxal alone. Image credit: Estelle Heitz.
“Manuka honey, a monofloral honey derived from the nectar of Leptospermum scoparium in New Zealand, has attracted considerable attention because of its broad-spectrum antimicrobial activity,” said Aston University researcher Jonathan Cox and his colleagues.
“Unlike other honeys, the antibacterial activity of Manuka honey is largely attributed to non-peroxide mechanisms.”
“Commercial Manuka honey is commonly classified using the Unique Manuka Factor (UMF) grading system, which reflects authenticity and the presence of key marker compounds.”
“The UMF grading system is independently certified and incorporates measurements of MGO, leptosperin and dihydroxyacetone, alongside tests confirming the absence of adulteration.”
“UMF grades typically range from 5+ to 20+ or higher, with increasing grades generally associated with higher concentrations of MGO.”
“However, whether increasing UMF grade consistently translates into greater antibacterial activity remains unclear.”
Working with the honey producer Comvita, the study authors tested five grades of Manuka honey against four bacteria responsible for serious respiratory illness: methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae and Pseudomonas aeruginosa.
All grades of honey inhibited bacterial growth, and the effect grew stronger as UMF increased.
The two staph strains, including drug-resistant MRSA, were especially vulnerable, requiring far less honey to stop their growth than the two more hardy Gram-negative species.
A central question the researchers set out to answer was why Manuka honey works better than ordinary honey, given that both are essentially concentrated sugar solutions capable of dehydrating bacterial cells through osmotic stress.
To test this, they compared the honey against a sugar solution matched to its exact carbohydrate makeup.
In every case, the honey suppressed bacterial growth far more effectively than sugar alone, indicating that osmotic pressure could not be the whole story.
When they created solutions containing MGO at concentrations matching those naturally found in each honey grade, those solutions had some antibacterial effect, but consistently less than the whole honey.